Collision code trace

[mlangsdorf]

vehicle::act_on_map() -- called once per tile of movement
map::move_vehicle( veh, tripoint( dx, dy ), movedir )
vehicle::precalc_mounts()
std::vector collisions;
do {
collisions.clear()
vehicle::collision( collisions, dp, false )
for structure parts:
coll = vehicle::part_collision()
figure out if we're hitting a vehicle, terrain/furniture, or a creature
calculate collision energy, relative mass, etc.
do {
bash furniture until it breaks or the vehicle stops
smash creatures
} while collision velocity doesn't change sign
return damage inflicted (but don't damage the vehicle I think?)
collisions.push_back( coll )
return !collisions.empty()
for vehicle_collisions
map::vehicle_vehicle_collision()
/* something */
for non-vehicle collisions
veh.damage( impact part )
veh.damage_all( impact part )
while moving and collisions
finish move_vehicle()